Hi! I've tried to give you as good answers as possible below: Has set English (en-GB) as first language in the language list on page "Manage Web Site Languages". This should make it default language? There are several ways to set the "default" language. One way is to, as you say, make sure that the language is first in the list. Another way is to define a domain-language mapping. This post describes this more: http://www.episerver.com/en/EPiServer_Knowledge_Center/Developer-Forum2/EPiServer-Developer-Forums-/EPiServer-CMS-version-5/13015/ Can I change the Root page from having English(en) as it's language to (en-GB)? Depending on what you really want to achive there are some different answers: 1. If you want to move/retag all content to another culture: I tested to change the language branch table by removing the row for en-GB and then renaming the en language branch to en-GB (columns LanguageID and SystemIconPath). As far as I can see this has tagged the content as en-GB. 2. If you just want to change language branch for a subset of pages: We have two different tools that are available from the support. One changes master language for a subset of pages and the other tool change language branch for the content for a subset of pages. This tool was developed for EPiServer 4 and is still in "beta" phase. The plan is to have these as available admin functions but we have not decided when this is going to be implemented. (A disclaimer: I do not know if these have been tested for EPiServer CMS yet) Should the languageXX.xml file be named languageGB.xml for english (en-GB)? You can name the file whatever you want as long as is resides in the language folder. The only thing that matters is that the id(s) for the language(s) in you file match the language code. We currently have a bug that limits you to defining the language code as a neutral culture. This means that the language code in the language files needs to be defined withs two character until we correct this (for instance "en" instead of "eb-GB".